As wireless communications systems continue to evolve and improve, it may be common for a service area to be served by multiple wireless communications systems as service providers upgrade equipment while keeping older equipment operational for compatibility purposes as well as improved coverage. In order to maximize user equipment (UE) flexibility, UE may be operable in the multiple wireless communications systems. UEs may also be referred to as mobile stations (MS), terminals, users, communications devices, and so forth.
FIG. 1 illustrates a wireless communications system 100. Wireless communications system 100 includes a first wireless communications network 105 that makes use of a first radio access technology (RAT_1) and a second wireless communications network 110 that makes use of a second radio access technology (RAT_2). RAT_2 may be an older access technology that has been in use for a longer period of time, hence second wireless communications network 110 may have a larger coverage area than first wireless communications network 105. For example, RAT_2 may be a first or second generation access technology, such as code division multiple access (CDMA), CDMA2000, high rate packet data (HRPD), and so on, while RAT_1 may be a third or fourth generation access technology, such as long term evolution (LTE), LTE-Advanced, WiMAX, and so forth.
Wireless communications system 100 also includes UEs, such as UE 115, UE 120, and UE 125. The UEs may be capable of operating in both first wireless communications network 105 and second wireless communications network 110. The UEs may also be capable of changing service from first wireless communications network 105 to second wireless communications network 110, and vice versa. This is commonly referred to as a handover.
As shown in FIG. 1, UE 115 may be operating in a center of first wireless communications network 105 (which is also in a coverage area of second wireless communications network 110), and since first wireless communications network 105 may offer higher data rates, more functionality, etc., UE 115 may prefer to be served by a controller of first wireless communications network 105. UE 120 may be operating in a coverage area of second wireless communications network 110 that is outside of a coverage area of first wireless communications network 105, so UE 120 may be served by a controller of second wireless communications network 110 by default.
A controller of a wireless communications network may control transmissions to and from a UE that it is serving. For example, the controller may receive a transmission intended for the UE and store (buffer) the transmission until it forwards the transmission to the UE. Additionally, the controller may control transmissions made by the UE by allocating network resources to the UE, without which, the UE may not be able to transmit. The controller may also be referred to as a base station (BS), base terminal station (BTS), NodeB, enhanced NodeB (eNB), and so forth.
UE 125 may be operating in a border cell (also referred to as a border cell scenario) of first wireless communications network 105, wherein UE 125 may be receiving transmissions from first wireless communications network 105 at low power levels. In such a situation, UE 125 may be a candidate for a handover from first wireless communications network 105 (also referred to as a current RAT) to second wireless communications network 110 (also referred to as an alternate RAT) if it is capable of receiving better service from second wireless communications network 110.